Pultrusion is an automated and continuous method of forming composite parts. Glass or other reinforcing fibers are impregnated with thermosetting resin and pulled through a forming guide and a heated die. The forming guide orients the fibers to be properly placed in the heated die to insure that the pultruded part is properly reinforced across its shape. The heated die cures and solidifies the resin around the reinforcing fibers, thus forming the composite part. The pultruded part, having a profile shape, is continuously pulled out of the heated die by a puller.
Pultrusion allows for composite parts to be produced with complex profile shapes, diverse resin mixtures, and numerous reinforcement types. These features make pultrusion a versatile process where shape and properties can be tailored to a specific application.
The surface appearance of a pultruded part depends on many factors. For smooth and decorative surfaces, low profile additives and surfacing veils are used to produce a smooth surface. Low profile additives are added to the mixture to counter resin shrinkage and reduce fiber imprint. Surfacing veils cover the reinforcing fibers with a cloth-like material that is typically made with nylon fibers, polyester fibers, or glass fibers. Surfacing veils can be pigmented or dyed to give color or patterns to the pultruded surface. However, because the veils are covered with a thin layer of cured resin, the color imparted on the pultrusion from the dyed veil is often hazed and lighter that the intended color. The hazing comes from a by-product of the shrinkage control mechanism of the low profile additive. If the low profile additive is removed, imparted colors are richer but fiber imprint is easily noticeable and overall dimensional shrinkage can be severe.
Moreover, this approach results in a minimally phosphorescent pultruded part because the haze from the resin layer on top of the surfacing veil scatters light and reduces the ability of the phosphorescent pigment to charge and to emit. In addition, the resin layer is also exposed to the UV needed for charging the phosphorescent pigments, resulting in yellowing and degradation. The surfacing veil also does not impart the necessary phosphorescent pigment surface concentration needed for effective glow-in-the-dark properties because a high concentration of pigment on the surfacing veil reduces the ability of the resin mixture to properly wet-out the veil.
Color can also be imparted onto a pultrusion surface by the addition of pigments to the mixture formulation. The mixture formulation contains resins, low profile additives, lubricants, fillers, and other special function additives. The hazing from the low profile additive also affects this imparted color from the mixture pigments. The hazing has the effect of lightening the color of the cured pultruded part. Cost-effective pultruded parts are also not UV stable enough for most outdoor applications. Long term exposure to UV can yellow and degrade the surface of the pultrusion. Because of these limitations, pultruded parts generally require protective coatings on them to give the necessary decorative finish and weather resistance.
Also, applying the pigment to the resin mixture requires far more pigment than is needed for critical surface concentration of phosphorescent pigment. Phosphorescent pigments can cost as much and one hundred times more per pound as the rest of the resin mixtures; therefore applying phosphorescent pigments in this manner is prohibitively expensive.
What is needed is glow-in-the-dark pultruded part and a method of making a glow-in-the-dark pultruded part that possesses sufficiently strong glow intensity, is UV stable, and is cost effective.